Abstract:

The study aims to screen and obtain highly efficient biocontrol strains against tobacco root rot disease, providing germplasm resources for the biological control of tobacco root rot disease. Root rot fungi from diseased tobacco was isolated and purified by tissue separation method. The types of pathogenic bacteria were determined by morphological and molecular biological methods, and the biocontrol bacteria with good antagonistic effect against pathogenic bacteria were screened from tobacco planting soil, and their species were identified by molecular biological methods. The effect on tobacco root rot disease control and tobacco growth index was evaluated by plate confrontation and indoor pot test. The results showed that among the 6 fungi isolated and purified from diseased tobacco roots, only strain L1 could infect tobacco, exhibiting symptoms consistent with field infections and strong pathogenicity. It was identified as Fusarium oxysporum. 6 functional strains were screened via the plate confrontation method, among which bacterial strain B10 showed the highest inhibition rate (57.66%) against F. oxysporum and was identified as Bacillus velezensis B10. Pot experiments demonstrated that B10 effectively reduced the incidence of tobacco root rot, achieving a control efficacy of 63.63%, outperforming the chemical agent carbendazim (27.27%). Additionally, strain B10 promoted tobacco growth: compared to the control (CK), it significantly increased maximum root length, plant height, stem base diameter, aboveground fresh weight, and root fresh weight by 17.32%-37.67%. The B. velezensis B10 strain screened in this study effectively inhibits F. oxysporum, reduces the incidence and severity of tobacco root rot, and significantly promotes tobacco growth, demonstrating promising biocontrol potential.

Key words: flue-cured tobacco, root rot disease, Bacillus velezensis, antagonistic bacteria, biological control, promoting effect, disease suppression effect